Various human activities, such as activities by a wheelchair user, involve repetitive motions of the arms. For example, pushing oneself in a wheelchair, rowing, push-ups and pull-ups, and assembly-line tasks may all involve repetition of a sequence of motions using the hands, arms, and wrists. A wearable device may be worn on the hand, wrist, or arm of the person performing the activity. It may be desirable to track activity by a wheelchair user for health, safety, or productivity reasons.